Hi Sebastian,
seems like we shared same problem. I'm preparing for cert for some time now too.
If You must use EPM_MODEL then you can try and generate some data in Sap system and then load to Hana.
1.First check out SWND* tables that you need (in SE11 or SE16n). Empty I guess.
2.Generate data with transaction SEPM_DG
partly explained http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/d0a7f673-59da-2f10-6e8b-bc7fe5dd4d0f?QuickLink=index&…
Some tables will be filled, for example SNWD_BPA_CONTACT , some not, others use sunscreen
There is a way to fill them all I guess. Some data You can fill on your own if you need. Its just a few tables and you need few records per any of them.
3. You then use one of Data Prov Tools Hana universe gave us....IMPORT is good enough (import flat file scenario)..simple and you dont need extra tools.
For each table:
-Go to SE16n, download data to xls (Change header names if necessary) - or write Abap code to do that.
-Import xls to Hana - Sap Hana Studio: File->Import ->SapHana Content Folder "Data from Local file" )
Change data types if necessary..just go on.
This way, model for all tables will be loaded (tables created), data for ones that you filled with data. ANd there's your EPM_MODEL 
But my advice would be - dont bother. SHINE model is perfect for simple examples even from HA300.
Any table from HA300 examples has its similar table in SHINE that can be used instead...there's no NODE_KEY, PARENT KEY in Shine tables..but those fields are only burden in those examples).
Sometimes You will have to omit some fields (take another one instead), sometimes you'll have to JOIN with third table to get text or something, but it will only deepen your understanding of data modelling in HANA.
For me exercises then become true, and not just "going thru the motions" just to finish them
I wish you luck in certification and have fun preparing. I am enjoying myself, hope you are too.
I 
Hana.
Hope this helps.
Take care,
Dubravko.